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Long vs. Short

What’s the difference?

In traditional Short Fibre Thermoplastics (SFT) the glass fibres are in effect milled during the compounding process resulting in a retained fibre length (RFL) of between 0.2-0.9mm. Long Fibre Thermoplastics (LFT) on the other hand are manufactured in a way that the fibres are the full length of the pellet and only limited by the injection moulding machines’ ability to accept the pellets. Generally pellets and hence RFL are 10-15mm long.

Long vs. Short

Why does it matter?

The skeletal structure provided by longer fibres (clearly seen when the polmer structure is burned away, shown right) is the source of the performance advantage gained through LFT technology.

When an external stress is applied to the part, the energy is transferred to the 3 dimensional structure and distributed over a wider area. This is clearly demonstrated by the far superior impact toughness of LFT vs SFT. In addition to improved impact, the advantages extend to improved tensile, flex & creep properties over a wide range of temperatures.

Furthermore, because the fibres form an interlocking 3 dimensional structure, issues arising from an-isotropic shrinkage are negated giving LFT the ability to mould dimensionally stable parts in simple and complex geometries alike.

Do I have to do anything different?

Yes! and Duromer can assist you. It is important to take fibre orientation into account when gating to ensure you get the maximum benefit from your LFT compound.

You must also ensure that your injection moulding machine is equipped with a high flow screw tip assembly to prevent unnecessary fibre attrition and keep back pressure to a minimum. Couple this with slower injection speeds and lower back pressure where feasible to ensure the best possible results.


LFT offers performance benefits over SFT that make the concept of metal replacement more of a reality. In a world where everything seems to be on a weight loss program, LFT opens up new opportunities to light weight and thin wall your products to save on materials and your carbon footprint.